We were told to remember this day WTF nothing happened . when will if ever , will this shit stop I thinking never
I suspect we were told to remember it because something happened that wasn't obvious at the time but will be significant to what comes next.
You don't have to tell people to remember a day if something massive happens that everyone is aware of. Imagine someone telling people on 9/11: "Remember this day." They'd have thought you were out of your mind.
Say I knew someone was going to win the lottery on Sunday. I might tell them to remember Friday because I know that will be the last day they ever have to go to a job they hate. On Saturday, they'd be thinking, 'Why was I told to remember yesterday?'